1. Field of the Invention
The present invention generally relates to a vehicle drive force control apparatus in which either the front wheels or the rear wheels are driven by an engine and the subordinate drive wheels can be connected to and driven by an electric motor. More specifically, the present invention is well-suited to a four-wheel drive vehicle having main drive wheels that are driven by an engine and subordinate drive wheels that can be braked and driven by an electric motor.
2. Background Information
One example of a so-called motor-driven four-wheel drive vehicle in which the front wheels (hereinafter also called “main drive wheels”) are driven by an engine and the rear wheels (hereinafter also called “subordinate drive wheels”) are driven by an electric motor in an auxiliary manner is disclosed in Japanese Laid-Open Patent Publication No. 2001-253256. The vehicle disclosed in that publication is designed such that a clutch (connecting device) installed between the rear wheels and the electric motor is released when the traveling speed of the vehicle reaches or exceeds a prescribed value, thereby preventing the electric motor from rotating at a speed exceeding its maximum tolerable rotational speed.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved vehicle drive force control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.